1. Field of the Invention
The present invention relates in general to an ink cartridge for supplying, with ink, an ink-jet printing head which performs printing by ejecting the ink, and an ink-jet printer including the ink cartridge.
2. Discussion of Related Art
There is known an ink-jet printer arranged to perform printing by ejecting ink through nozzles onto a recording medium. Such an ink-jet printer is equipped with an ink cartridge removably mounted thereon, as disclosed in JP-A-2001-328279 (FIG. 1, in particular). In such an ink cartridge, however, where a vent hole (air introducing hole) of an ink storing chamber (ink tank) is located above the ink storing chamber, the surface of the ink in the ink storing chamber is exposed to an atmosphere, in other words, an atmospheric pressure acts on the ink surface. In this arrangement, when the level of the ink surface decreases with consumption of the ink, a back pressure of the ink acting on the nozzles varies. The variation in the back pressure of the ink which acts on the nozzles may adversely influence an accuracy of ejection of the ink from the nozzles. Hereinafter, “the level” refers to a “height level”.
In view of the above, the ink-jet printer is generally equipped with a mechanism for suppressing or inhibiting the variation in the back pressure of the ink. One example of such an ink-jet printer is disclosed in U.S. Pat. No. 6,702,427 B2 (FIG. 4, in particular) corresponding to JP-A-2002-307711. The disclosed ink-jet printer is equipped with a buffer tank which is connected to nozzles and in which ink is stored with its surface level kept approximately constant. The buffer tank has an ink supply tube in the form of a hollow needle for supplying the buffer tank with the ink in the ink cartridge and an air introducing tube in the form of a hollow needle for introducing air into the ink cartridge. The ink supply tube and the air introducing tube are disposed so as to extend through an upper wall portion of the buffer tank. Within the buffer tank, the ink supply tube extends downwardly farther than the air introducing tube, near the bottom of the buffer tank.
In a state in which the ink is not ejected from the nozzles, the ink surface is in the vicinity of a lower end of the air introducing tube. In this state, a meniscus of the ink is formed inside the lower end of the air introducing tube, so that the air is not introduced through the air introducing tube into the ink cartridge. Accordingly, the ink is not supplied from the ink cartridge to the buffer tank. When the ink is ejected from the nozzles, the ink is supplied to the nozzles through an ink supply hole formed at the bottom of the buffer tank and the level of the ink surface in the buffer tank decreases, so that the ink surface separates from the lower end of the air introducing tube and the meniscus in the air introducing tube is broken. As a result, the air enters the air introducing tube and is accordingly introduced into the ink cartridge. Simultaneously, the ink is supplied from the ink cartridge to the buffer tank via the ink supply tube. When the surface level of the ink in the buffer tank reaches in the vicinity of the lower end of the air introducing tube, the air is not allowed to be introduced into the ink cartridge through the air introducing tube, whereby the supply of the ink into the buffer tank stops. In this case, the variation in the back pressure acting on the nozzles is not influenced by the amount of the ink remaining in the ink cartridge, but influenced only by the amount of the ink remaining in the buffer tank whose volume is small, resulting in suppression of the variation in the back pressure.